A circuit board is constructed by forming a circuit pattern including many circuit boards on one large substrate and cutting the substrate into multiple circuit boards. At least one pair of guide holes is opened in the substrate and fitted on guide pins provided on a cutting device to position and cut the substrate. Therefore, the guide holes serve as a reference for determining cutting positions and should be opened in precise positions.
A boring machine used for forming the guide holes captures an image of positioning marks formed on the substrate with an X-ray camera, processes the image, acquires boring positions, and moves a drill to the acquired positions for boring.
For example, Unexamined Japanese Patent Application Kokai Publication No. H9-57695 discloses a boring machine of the above type.
The above type of boring machines use an X-ray, which is harmful to humans. Therefore, the prior art boring machines comprise a shielding member covering the entire X-ray operation area and a lead-containing sheet cut into strips and provided at the entrance for the substrate so as to prevent the X-ray from leaking outside.
As shown in FIG. 8A, raised edges (burrs) 102 consisting of layers of copper foil and adhesive remain at the sides of a board 101 to be bored.
The raised edges 102 raise up the X-ray shielding skirt at the entrance and cause the X-ray to leak as the printed board 101 enters the boring machine.
The same incident may occur in various devices using an X-ray for processing such as X-ray processing devices using an X-ray for positioning in the course of stacking and heating/laminating single-layer printed boards.